1. Field of the Invention
The present invention relates to a method of separating fatty alcohols by distillation from solutions comprising alkyl polyglycosides (APGs) and fatty alcohols.
2. Description of the Background
Alkyl polyglycosides are nontoxic and readily degradable surfactants. Therefore they are used as detergents, cleaning agents, emulsifiers, and dispersants. They have the desired interfacial characteristics only if the alkyl groups have at least 8 carbon atoms.
Alkyl polyglycosides with long-chain alkyl groups are generally manufactured by single-stage or multistage syntheses.
A single-stage synthesis is described, e.g., in German Pat. App. No. P 41 01 252.6.
A two-stage method is disclosed, e.g., in Eur. OS 0,306,652, in which first an n-butyl glycoside is prepared by glycosidation of n-butanol, followed by a trans-glycosidation with a long-chain alcohol to produce the desired long-chain APG.
After completion of the reaction, the APGs are present as solutions in long-chain alcohols. The alcohols must then be separated out if a product is desired which yields a clear solution when dissolved in water.
According to Eur. Pat. 0,077,167, the excess alcohol should be removed as soon as possible. During removal of the alcohol, the thermal stress on the reaction products should not be excessive. In fact the reference examples describe the removal of alcohols by distillation in vacuum. The apparatus used for this, and the conditions, are not specified, however.
In Eur. Pat. 0,092,876, fatty alcohols are removed by distillation from solutions comprising alkyl polyglycosides and fatty alcohols using a thin-layer evaporator. For this method, the Reynolds number should be&gt;20,000.
The consequence of the requirement of a high Reynolds number is that in the event of highly viscous products the layer thicknesses must be high and the rpm of the rotor in the thin-layer evaporator must be high. This results in the formation of products by cracking which stain the evaporator, and premature wear of the moving parts. Accordingly, a need continues to exist for a method by which fatty alcohols can be removed by distillation which saves and protects the product even in the case of highly viscous APG solutions.